Elastomeric products which have to withstand high dynamic loads, such as drive belts, transport belts or flexible tubes, must satisfy high requirements as to wear resistance, modulus of elasticity, tensile strength, tear resistance, aging resistance, flexibility in cold temperatures, heat build-up and chemical and oil resistance. Additional requirements for drive belts include low noise development and retention of desired mechanical characteristics at high temperatures. Overall, the mentioned characteristics should contribute to a long service life of the elastomeric product.
In order to satisfy these high requirements, especially with respect to heat resistance, radical cross-linked, that is, peroxide cross-linked rubber mixtures, are utilized for many elastomeric products, especially for drive belts. These radical cross-linked rubber mixtures are based, for example, on hydrogenated nitrile rubber (HNBR), ethylene-propylene-diene rubber (EPDM) and/or ethylene-propylene rubber (EPM). To increase the cross-linking density and to improve the characteristics of the vulcanized product of radical cross-linked rubber mixtures it is further known to add co-agents/co-activators, such as tri-allyl compounds or reactive acrylate derivates, to the mixture. As co-agents, for example, metal salts of α,β-unsaturated carboxylic acids are suggested, such as zinc salts of acrylic acid or methacrylic acid.
In European patent publication 0 866 834 B1, for example, drive belts having a long service life are described which are based on EPDM and/or EPM and include 32 to 100 phr of at least one metal salt of an α,β-unsaturated carboxylic acid, preferably zinc diacrylate.
European patent publication 1 205 515 A1 discloses the use of 1 to 30 phr of at least one metal salt of an α,β-unsaturated carboxylic acid, especially zinc dimethacrylate, in mixtures of ethylene-alpha-olefin rubber, such as EPDM and EPM.
Japanese patent publication 2981575 B2 discloses drive belts which include a peroxide cross-linked rubber mixture and the rubber mixture is based on a saturated rubber (for example, EPM) and includes staple fibers and a metal salt of an ethylenically unsaturated carboxylic acid. In this publication, it is further described that, in addition to the direct use of the metal salts of the ethylenically unsaturated carboxylic acid, these salts can be generated in situ in that suitable metal salts, such as carbonates, oxides or hydroxides, and the ethylenically unsaturated carboxylic acid are added to the mixture and react there to the corresponding metal salt of an ethylenically unsaturated carboxylic acid.